Partial support of laravel 6

[JonathanMM]

Hello,
I tried to update cachet, with using laravel 6. This update fix #71 since cachet can run now with PHP 7.4 (and probably PHP 8.0, but I didn't test it).
BUT, some things are broken, I have limited knowledge in laravel (I never use it before today :) ). For example, if a component have an issue registered in cachet, the homepage is broken (well, since it is the main purpose of cachet, I think this error is critical :) ).
Works on this PR:

• phpunit (tests runs, but I worked on a VM with basic resources, I didn't execute all tests)
• debug console
• install setup
• dashboard (the redirect to login page didn't work, go directly to /auth/login)
• homepage with empty data

I hope this PR can be helpful for other developer who knows laravel.